Poly α-olefins (polyalphaolefins or PAO) comprise one class of hydrocarbon lubricants which has achieved importance in the lubricating oil market. These materials are typically produced by the polymerization of α-olefins in the presence of a catalyst such as AlCl3, BF3, or BF3 complexes. Typical α-olefins for the manufacture of PAO range from 1-octene to 1-dodecene. It is known to make polymers using higher olefins, such as 1-tetradecene, as described in WO 99/38938, and lower olefins, such as ethylene and propylene including copolymers of ethylene with higher olefins, as described in U.S. Pat. No. 4,956,122. Oligomerization is typically followed by fractionation and by a step of hydrogenation to remove unsaturated moieties in order to obtain the desired product slate. In the course of hydrogenation, the amount of unsaturation is generally reduced by greater than 90%.
PAOs are commonly categorized by the numbers denoting the approximate viscosity, in centistokes (cSt), of the PAO at 100° C. PAO products may be obtained with a wide range of viscosities varying from highly mobile fluids with a nominal viscosity of about 2 cSt at 100° C. to higher molecular weight, viscous materials which have viscosities exceeding 100 cSt at 100° C. Viscosities as used herein are Kinematic Viscosities determined at 100° C. by ASTM D-445, unless otherwise specified. The term “nominal” as used herein means that the number has been rounded to provide a single significant figure.
PAOs may also be characterized by other important properties, depending on the end use. For instance, a major trend in passenger car engine oil usage is the extension of oil drain intervals. Due to tighter engine oil performance, a need exists for low viscosity PAO products with improved physical properties, e.g., evaporation loss as measured by, for instance, Noack volatility, as well as excellent cold weather performance, as measured by, for instance, pour point or Cold Crank Simulator (CCS) test. Noack volatilities are typically determined according to ASTM D5800; pour points are typically determined according to ASTM D97; and CCS is obtained by ASTM D5293.
PAOs are normally produced via cationic oligomerization of linear alpha olefins (LAOs). Low viscosity PAOs have been produced by BF3-catalyzed oligomerization based on 1-decene for many years. Processes for the production of PAO lubricants have been the subject of numerous patents, such as U.S. Pat. Nos. 3,149,178; 3,382,291; 3,742,082; 3,780,128; 4,045,507; 4,172,855; and more recently U.S. Pat. Nos. 5,693,598; 6,303,548; 6,313,077; U.S. Applications 2002/0137636; 2003/0119682; 2004/0129603; 2004/0154957; and 2004/0154958, in addition to other patent documents cited herein. PAOs are included as the subject of numerous textbooks, such as Lubrication Fundamentals, J. G. Wills, Marcel Dekker Inc., (New York, 1980), and Synthetic Lubricants and High-Performance Functional Fluids, 2nd Ed., Rudnick and Shubkin, Marcel Dekker Inc., (New York, 1999).
The properties of a particular grade of PAO are greatly dependent on the α-olefin used to make that product, as well as the catalyst used and other process details. In general, the higher the carbon number of the α-olefin, the lower the Noack volatility and the higher the pour point of the product. PAO's having a nominal viscosity at 100° C. of 4 cSt are typically made from 1-decene and have a Noack volatility of 13-14% and pour point of <−60° C. PAO's having a nominal viscosity at 100° C. of 6 cSt are typically prepared from 1-decene or a blend of α-olefins and have a Noack volatility of about 7.0% and pour point of about −57° C. PAOs made from LAOs that have molecular weights higher than 1-decene typically have higher pour points but lower viscosities at low temperatures. These effects are generally caused by waxiness of the oligomerized molecules. PAOs made from very low molecular weight LAOs such as 1-hexene, also have high pour point as well as high viscosity at low temperature. These effects could be attributed to the formation of branched molecules coupled with viscosity increases. In the past, when oligomerizing LAO mixtures, mixtures of high and low molecular weight LAOs are generally used in an attempt to offset the properties and arrive at PAOs roughly similar in properties to C10-based oligomers.
U.S. Pat. No. 6,071,863 discloses PAOs made by mixing C12 and C14 alphaolefins and oligomerizing using a BF3-n-butanol catalyst. While the biodegradability of the product was reported to be improved when compared with a commercial lubricant, the pour point was significantly higher.
In U.S. Pat. No. 6,646,174, a mixture of about 10 to 40 wt. % 1-decene and about 60 to 90 wt. % 1-dodecene and are co-oligomerized in the presence of an alcohol promoter. Preferably 1-decene is added portion-wise during the single oligomerization reactor containing 1-dodecene and a pressurized atmosphere of boron trifluoride. Product is taken overhead and the various cuts are hydrogenated to give the PAO characterized by a kinematic viscosity of from about 4 to about 6 at 100° C., a Noack weight loss of from about 4% to about 9%, a viscosity index of from about 130 to about 145, and a pour point in the range of from about −60° C. to about −50° C.
In U.S. Pat. No. 6,824,671. A mixture of about 50 to 80 wt. % 1-decene and about 20 to 50 wt. % 1-dodecene are co-oligomerized in two continuous stirred-tank reactors in series using BF3 with an ethanol:ethyl acetate promoter. Monomers and dimers are taken overhead and the bottoms product is hydrogenated to saturate the trimers and higher oligomers to create a 5 cSt PAO. This product is further distilled and the distillation cuts blended to produce a 4 cSt PAO containing mostly trimers and tetramers, and a 6 cSt PAO containing trimers, tetramers, and pentamers. The lubricants thus obtained are characterized by a Noack volatility of about 4% to 12%, and a pour point of about −40° C. to −65° C. See also U.S. Pat. No. 6,949,688. (Note that, as used in the present specification, “dimer” includes all possible dimer combinations of the feed, e.g., for a feed comprising C10 and C12, “dimers” comprise a mixture of oligomers containing C20, C22, and C24, otherwise referred to as “C20 to C24 fractions”).
U.S. Patent Application 2004/0033908 is directed to fully formulated lubricants comprising PAOs prepared from mixed olefin feed exhibiting superior Noack volatility at low pour points. The PAOs are prepared by a process using an BF3 catalyst in conjunction with a dual promoter comprising alcohol and alkyl acetate, and the products are the result of blending of cuts.
U.S. patent application Ser. No. 11/338,231 describes trimer rich oligomers produced by a process including contacting a feed comprising at least one α-olefin with a catalyst comprising BF3 in the presence of a BF3 promoter comprising an alcohol and an ester formed therefrom, in at least one continuously stirred reactor under oligomerization conditions. Products lighter than trimers are distilled off after polymerization from the final reactor vessel and the bottoms product is hydrogenated. The hydrogenation product is then distilled to yield a trimer-rich product. In preferred embodiments, the feed comprises at least two species selected from 1-octene, 1-decene, 1-dodecene, and 1-tetradecene.
A document entitled “Next Generation Polyalphaolefins—the next step in the evolution of synthetic hydrocarbon fluids”, Moore et al., Innovene USA LLC Nov. 22, 2005 revision; posted Nov. 22, 2005 at www.innovene.com (last visited Mar. 1, 2006) discusses PAOs based on C10 PAOs and C12/C14 PAOs.
It is becoming increasing more difficult for the industry to keep up with the demand for lubricating basestocks having properties similar to C10-based PAOs. It would be highly beneficial if the range of linear alphaolefins that could be used to make such basestocks could be extended. The present inventors have surprisingly discovered that under appropriate conditions compositions comprising 1-hexene may be oligomerized to yield useful basestocks having properties, in preferred embodiments, similar to 1-decene-based PAOs.